1. Field of the Invention
High-modulus filaments and rods are produced from crystalline organic polymers by a process of ultra-drawing under high hydrostatic pressure.
2. Description of the Prior Art
Important physical properties of crystalline organic polymers can be greatly improved by mechanically working the polymers to cause alignment of the chain macromolecules. For instance, high-density polyethylene, when formed into filaments highly oriented along the fiber axis, develops a tensile modulus of elasticity (Young's modulus) 70- to 100-fold greater than that exhibited in the isotropic solid state. The modulus at room temperature exceeds 50 GPa (GigaPascals) and may reach 100 GPa. The latter is close to one-third the theoretical limit for a carbon-to-carbon molecular chain and on a weight-for-weight basis exceeds that even of drawn steel wire.
Such filaments have been produced by growing them from dilute solution or by melt or solid-state extrusion through a capillary. These methods are of interest only in laboratory research. Capillary extrusion, for instance, is very slow, making only a few centimeters of filament per hour.
Another known procedure of making strong filaments is that termed "ultra-drawing". In this, a solid body of the polymer, usually somewhat elongated, is stretched or drawn to extreme degree. The draw ratio (length after drawing/length before) should be at least 20, preferably 30 or more, in the case of polyethylene. Such ultra-drawing does make product of greatly increased modulus. However, the filaments produced by ultra-drawing as heretofore conducted have a high content of internal voids, often exceeding 20 percent by volume. The occurrence of such voids renders the product opaque and prevents attainment of the full increase in modulus and other desirable properties of which the polymer is capable.
Further discussion of these factors, with bibliography, appears in articles by the present applicants, Polymer 20, 1078 (1979) and J. Poly. Sci., Polym. Phys. Ed. 17, 1611 (1979).